1. Field of the Invention
The present invention relates to a method and an apparatus for sample injection in gas chromatography.
2. Description of the Related Art
In a conventional apparatus for sample injection in gas chromatography, a vaporizing chamber is normally constituted from a thin, long, and straight glass tube whereto the needle of a syringe is inserted from the upper end, known as a liner, and is provided with a metal bottom plate member for closing the opening formed on the lower end of the glass tube and for inserting the end of the separation column.
When such a straight glass tube is used, the injected sample reaches the lower end of the vaporizing chamber instantly, and it takes a long time until the sample that has reached the bottom plate member positioned on the lower end of the vaporizing chamber is vaporized, and goes to the (upper) end of the separation column positioned above the bottom plate member. This may cause the detection data to change. Also, when the sample contacts the metal surface of the hot bottom plate, chemical change may occur, causing significant change in the detection data.
In order to prevent this, silica wool is generally packed in the vaporizing chamber so that the injected sample does not reach the lower end of the vaporizing chamber instantly.
In such a system, however, the objective compound may adhere to the silica wool, and may be retained or decomposed.
Since the conventional apparatus has a constitution in which a separation column is connected to the lower end of a straight vaporizing chamber, a large volume of sample cannot be held in the vaporizing chamber in a liquid state, and there is a problem of difficulty of large-volume injection because the normal injecting volume is 1 to 2 xcexcl. Therefore, some large-volume injection systems with an increased injecting volume have been proposed. For example, in a system called on-column system, a pre-column is provided before a main column, a solvent in a sample is vaporized in the pre-column, and an objective compound is concentrated in the pre-column and transferred to the main column. In this system, however, a long pre-column is required, a solvent exhaust line must be provided, and the injection rate of the sample must be set accurately. In a system called baffle system, a solvent in a sample is vaporized on the surface of a baffle vaporizing chamber, an objective compound is concentrated on the surface of the vaporizing chamber and transferred to the column. However, this system is not suited for the analysis of low-boiling-point compounds, and a significant increase in injecting volume cannot be expected.
In view of the above-described situations, what the present invention is to solve is to provide a method and an apparatus for sample injection in gas chromatography that can significantly increase an injecting volume of a sample, and can analyze any of high-boiling-point compounds, low-boiling-point compounds, and compounds,decomposed by heat at a high accuracy.
The present invention can solve the above-described problems by using a method for sample injection in gas chromatography comprising the steps of injecting a sample through a curved or crooked sample path into a vaporizing chamber formed of continuous inner walls; temporarily holding the sample in a holding chamber provided in the vaporizing chamber; then vaporizing an objective compound; and introducing the objective compound into a separation column; or by using an apparatus for sample injection in gas chromatography comprising a vaporizing chamber, a syringe introducing portion installed above the vaporizing chamber, and a separation column connecting portion installed under the vaporizing chamber; in which the vaporizing chamber has a curved or crooked sample path and is formed with continuous inner walls, and comprises a holding chamber for temporarily holding the sample in the vaporizing chamber.
By using the vaporizing chamber having a curved or crooked sample path and formed with continuous inner walls as described above, the injected sample can be held temporarily in the vaporizing chamber, thus enabling the injection of a large volume of sample. By adjusting the temperature of the vaporizing chamber by supplying a heat medium such as heated air around the vaporizing chamber, the objective compound is vaporized, and the vaporized objective compound is introduced into the separation column for analysis.
By heating the sample held in the vaporizing chamber to first volatilize only the solvent and to discharge the volatilized solvent through a split vent; then adjusting the temperature in the vaporizing chamber to vaporize the objective compound; and introducing the objective compound into the separation column; the injecting volume can be increased, and the accuracy of the analysis can be improved as compared with the case where a sample is analyzed together with a solvent.
If the sample is easily decomposed by heat, by setting the initial temperature of the vaporizing chamber lower than the boiling point of the solvent in the sample; injecting the sample into the vaporizing chamber; slowly elevating the initial temperature of the vaporizing chamber to vaporize the objective compound; and introducing the objective compound into the separation column; even the sample easily decomposed by heat can be introduced into the separation column in a non-decomposed state.
If a large volume of the sample is injected, by setting the temperature of the vaporizing chamber lower than the boiling point of the solvent to maintain the injected sample in a liquid state in the holding chamber of the vaporizing chamber; discharging the volatilized solvent vapor through the split vent to concentrate the sample in the vaporizing chamber; then switching the mode to the splitless mode; and elevating the temperature of the vaporizing chamber to vaporize the objective compound: and introducing the objective compound into the separation column; the objective compound can be introduced into the separation column in the state where the physical change of the sample by an elevated temperature is avoided.
If the sample is derivatized for analyzing, by continuously injecting the sample and a derivatizing agent into the vaporizing chamber and holding in the holding chamber of the vaporizing chamber to derivatize the sample; and introducing the derivatized compound into the separation column; the analysis can be performed without touching the derivatizing agent.
By providing heating means and driving control means for controlling the drive of the heating means around the vaporizing chamber, the temperature in the vaporizing chamber can be maintained at the set temperature.
By constituting the heating means with an air chamber installed around the vaporizing chamber and a heated air delivery means for delivering heated air into the air chamber, the shape of the vaporizing chamber can be modified freely. In addition, compared with the constitution for heating with a conductive member made of a metal such as aluminum, any portions in the vaporizing chamber can be heated evenly and the cooling time can also be shortened.
The heated air delivery means may be constituted of a heater for warming the air, and a supply port installed on the wall surface forming the air chamber for supplying heated air warmed by the heater to the air chamber.
A needle of the syringe storing the sample penetrates the partition wall of the syringe introducing portion, and extends above the vaporizing chamber; and the syringe introducing portion comprises a carrier gas supply port and a septum purge vent.
The end of the separation column passes through the partition wall provided to the separation-column connecting portion, and extends below the vaporizing chamber.
A split vent is provided to the separation column connecting portion.
By constituting the vaporizing chamber from a single member, the number of members can be reduced comparing to the vaporizing chamber constituted by, for example, connecting two members.